Abstract
In this paper, we investigate the nonreciprocity of reflection in parity-time−symmetric (PT-symmetric) Cantor photonic crystals (PCs). Two one-dimensional PCs abiding by the Cantor sequence are PT-symmetric about the center. The PT symmetry and defect cavities in Cantor PCs can induce optical fractal states which are transmission modes. Subsequently, the left and right reflectionless states are located on both sides of a transmission peak. The invisible effect depends on the incident direction and the invisible wavelength can be modulated by the gain–loss factor. This study has potential applications in tunable optical reflectors and invisible cloaks.
Highlights
Optical invisibility has been extensively utilized for sensors, filters, and other civilian facilities [1,2,3]
Once the probing wavelength changes, the stealth effect will be greatly reduced. It is generally difficult for the absorption rate of light wave energy to reach a hundred percent [6] as there is energy surplus reflected by objects, meaning that it is necessary to find a new optical structure to realize the stealth of light waves and achieve a flexible adjustment to the stealth wavelength
The dielectric refractive index in non-Hermitian can be written as n = nr + i∗ni, where nr is the real part of the refractive index, ni is the imaginary part of the refractive index, and the letter i represents the imaginary unit
Summary
Optical invisibility has been extensively utilized for sensors, filters, and other civilian facilities [1,2,3]. Crystals 2022, 12, 199 mode, so that the maximum transmittance does not coincide with the left and right zero points of reflection [24].
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